In the cold, during the daytime, sound travles as well as it would at night on a warm day.
Wearing ashiko, or foot pattern creators, will make your foot pattern look like an animals. This can be fashioned from a thick soled type of footwear, like a combat boot. See if you can buy thick, tread less boots/shoes.
Guards tend to stay closer to a central warm point, and venture out much less.
Same with animals.
Getting hit has a stingy feeling to it; if it happens, you will know what I mean.
Bladed weapons are more efficient.
Bleeding from a large (6") area can induce shock from the cold.
People tend to fell more secure during the winter times; I really don't know why.
Trees become harder to use, as branches are more brittle.
Hand to hand combat works better as the pain is intensified, and cold bodies move slower.
Psychological warefare on guards in the winter leads to more fear.
Use of animals leads to a large amount of confusion.
It is easier to lose your night vision.
Bones are more brittle, and therefore harder to break.